Effective treatment of Gram negative bacterial infections has suffered due to a dearth of new antibiotics in the pharmaceutical pipeline. Only one novel antibacterial has been approved since 2006. Thus there is a clear unmet need for such therapies. Antibiotic resistance is one of the greatest threats to global human health. Thus, therapies with novel mechanisms of action that could circumvent resistance are highly desired. For example, sepsis or septic shock kills more than 200,000 people per year in the U.S. alone. Optimally, a sepsis therapeutic would serve as an antibiotic, as well as bind and neutralize the toxic effects of endotoxin (a.k.a., lipopolysaccharide, or LPS). The morbidity and mortality that results from severe infection in the U.S. alone is estimated at an annual cost of many billions of dollars. In the European Union the lost productivity and health care costs due to multi-drug resistant infections is estimated at 1.5 billion euros per year. New bioactive peptides that are effective against Gram negative infections and exhibit no or low toxicity would be a significant contribution to this global health crisis.
CAP37 (cationic antimicrobial protein of Mr 37 kDa) was originally identified as a component of the oxygen-independent killing mechanism of the human neutrophil (PMN) and was demonstrated to have strong bactericidal activity against Gram negative bacteria including Salmonella typhimurium, Escherichia coli, and Pseudomonas aeruginosa. Distinct from its effect on bacteria, the native CAP37 protein has potent regulatory effects on host cells. It is an effective regulator of cells of the mononuclear phagocytic system such as monocytes, microglia, and macrophages. It also regulates certain corneal epithelial, endothelial, and smooth muscle cell functions.
Structure-function analysis of CAP37 previously enabled the delineation of an antibacterial domain of the CAP37 protein, which was identified as residing in residues 20 through 44 of the native molecule. A peptide comprising this 25 amino acid sequence (i.e., CAP37 (20-44) SEQ ID NO: 7) mimicked the antimicrobial activity of the native molecule and extended its range of activity to encompass Staphylococcus aureus and Enterococcus faecalis, two Gram positive bacteria. The bactericidal activity of the peptide was pH dependent, with maximum activity obtained between pH 5.0 and 5.5. Derivatives of the natural peptide sequence of 20-44, wherein either of the cysteine residues at position 26 or 42 were replaced with serine residues (CAP37 (20-44)ser26 and CAP37 (20-44)ser42—SEQ ID NO:1 and 4, respectively), were also produced. However, commercialization of a peptide as a first-in-class anti-infective requires the ability to, for example, (1) scale-up the synthesis of the peptide, (2) achieve purity of preferably >90%, and (3) retain activity. The 20-44 peptide and previously-known substituted versions thereof could not be produced with these features. It is to novel peptide compounds that possess such properties and which comprise various portions of CAP37 proteins and derivatives thereof, as well as to methods of use of these compounds, that the presently disclosed inventive concepts is directed.